The present invention relates generally to vehicle suspension systems and, in an embodiment described herein, more particularly provides a suspension system for a dump truck which is to be connected to a paver using a truck hitch.
It is known to use a truck hitch to connect a paver to a dump truck. An example of such a truck hitch is described in U.S. Pat. No. 3,275,342, the entire disclosure of which is incorporated herein by this reference.
It is also known to use a steerable and liftable suspension on a dump truck which is to be connected to a paver using a truck hitch. An example of such a system is described in U.S. Pat. No. 5,718,443, the entire disclosure of which is incorporated herein by this reference. FIG. 1 of the present application corresponds to FIG. 1 of U.S. Pat. No. 5,718,443.
Depicted in FIG. 1 is a dump truck 10 having a liftable bed 12 for transporting material, such as paving material. The bed 12 is supported on a frame 14 which is, in turn, suspended above a road or ground surface 16 by multiple suspensions 18, including a steerable and liftable tag axle suspension 20. The suspension 20 helps to distribute the load transmitted from the truck 10 to the ground surface 16, for example, to comply with government regulations.
Unfortunately, in order for the truck 10 to be properly connected to a paver while the bed 12 is raised to dump the material from the bed into the paver, the tag axle suspension 20 must be retracted beneath the bed. This necessitates use of an expensive and heavy retraction mechanism 22. Furthermore, as the material is dumped from the bed 12, the load on the suspension 20 will decrease, causing a pneumatic cylinder 24 of the suspension to elongate and raise the rear end of the truck 10, thereby very undesirably changing the position of the bed 12 relative to the paver during the dumping operation.
This latter deficiency is attempted to be remedied by positioning a rigid support between the frame 14 and an axle 26 of the suspension 20 prior to the dumping operation, and then deactivating the pneumatic cylinder 24. However, this means that the suspension 20 becomes almost entirely noncompliant during the dumping operation. Most significantly, as the bed 12 is raised, a majority of the weight of the material and the bed is transferred to the rear of the truck 10 and, via the rigid support, directly onto the axle 26. This requires that a more expensive, heavier and higher capacity axle 26 be used in the suspension 20.
In addition, with the suspension 20 deployed as shown in FIG. 1, the effective wheelbase of the truck 10 is very long, making the truck less maneuverable. Also, due to the heavy retraction mechanism 22 and heavy axle assembly 26, as well as other components of the suspension 20, the truck 10 has a relatively large tare weight, and is expensive to produce and maintain.
In FIG. 2 another truck 11 is depicted which utilizes a steerable and liftable tag axle suspension 13. FIG. 2 of the present application corresponds to FIG. 1 of U.S. Pat. No. 6,116,698, the entire disclosure of which is incorporated herein by this reference.
The suspension 13 may be lifted up and out of the way when connecting a paver hitch to the truck 11, but it still suffers from much the same disadvantages as the truck 10 of FIG. 1. The suspension 13, including at least actuators 15, pivot arms 17 and an axle assembly 19, are very heavy and expensive to produce and maintain. When the suspension 13 is deployed, a wheelbase 21 of the truck 11 is greatly increased over the front-to-rear axle length 23 prior to deployment. Thus, the truck 11 is much less maneuverable with the suspension 13 deployed, the truck has a relatively large tare weight, and the suspension is expensive to produce and maintain.
Therefore, it may be clearly seen that a need exists for an improved suspension system for a dump truck which is to be connected to a paver. It is an object of the present invention to provide such a suspension system.